Nutritional Studies on Pecans [Carya illinoinensis L. (Wangenh.) C. Koch] Growing in Irrigated Alkaline Soils

Abstract

Annual application of N at rates of 118 (118N), 236 (236N), and 354 (354N) kg•ha⁻¹ on 35 year old 'Western Schley' pecan trees during four years had little effect on mineral composition and foliar N. No differences in yield, nut quality, and reproductive characteristics were found. Alternate bearing intensity in four consecutive years was 37, 33 and 28% in 118N, 236N, and 354N, respectively, with a significant linear response. Rates from 118 to 236 kg N•ha⁻¹ satisfy N needs for pecan in irrigated pecan orchard of the southwest of United States. The effect of one-time banding of zinc sulfate (74 kg Zn•ha⁻¹) and zinc-EDTA (19 kg Zn•ha⁻¹) was evaluated over a period of four years on ‘Wichita’ pecans growing in alkaline soil. Significant differences in foliar Zn levels were found one month after application of Zinc-EDTA. Differences also were noted during the next three years on approximately 25% of the sampling dates. Yield, leaflet area, and trunk cross sectional area were not affected. Zinc-EDTA increased Zn uptake by 'Wichita' pecan trees in alkaline conditions during three years. A field study indicated that manure or manure plus Zn increased foliar Zn levels in pecans after two years of annual applications. Manure (24 ton ha⁻¹) plus zinc sulfate (258 kg Zn•ha⁻¹ as zinc sulfate) treatment had the highest foliar Zn levels. No differences were observed in trunk growth, leaf area, leaf weight, nut filling, and yield. Manganese toxicity symptoms are exhibited when leaf Mn levels are higher than 1700 μg•g⁻¹ during the standard date sampling of July and affected reproductive characteristics and leaf and shoot growth. More severe visible symptoms include delayed budbreak and die-back of young shoots. In potted pecan trees, zinc EDTA treated trees had a foliar Zn of 244 μg•g⁻¹, in foliar sprayed trees (eight foliar sprays of a combination of zinc sulfate and UAN32) had 140 μg•g⁻¹, and in control trees had 33 μg•g⁻¹. Soil adsorption isotherms showed that of the three fertilizers evaluated Zn sulfate was adsorbed most strongly by the soil (1.5 mg Zn•g⁻¹ of soil). Soil adsorption from Zn EDTA solutions was insignificant.